No Common Denominator

All three victims had been young middle-class women; but other than that, no common denominator appeared to link them—not occupation, not background, not religious affiliation, not business associates or friends or doctors. Although all three had been attractive, their physical features had varied as well: Baek Eunhye, dark-haired and pale-skinned; Ahn Si-ha, dyed red hair and freckle-faced; and Shin Dong-mi her hair dyed blond. 

As far as Kim Hyeok could tell, the three women had nothing in common except the fact that they were young and vital and alive. Presumably that had been enough.